Because of several problems of fossil fuel energy with high cost and greenhouse effect, solving energy issue becomes an important task. The power generation of solar cells are applied by infinite solar energy and do not need fossil fuel, thus, solar cells now are utilized in satellite, space technology, and mobile communication. In view of energy saving, demands of the effective resource use and environmental pollution preventing, solar cells increasingly become attractive energy generators.
In 1954, the first inorganic solar cell formed on silicon (Si) is produced by Bell Laboratory in America, and such solar cell can transfer the solar radiation to electrical energy by photoelectric effect. However, the cost of the common solar cell formed on silicon wafer is higher than that of the others traditional power generation method (ex. fossil fuel thermal power plant), and doesn't meet the requirement of the production cost. Especially, the cost of solar cell formed on mono-crystalline silicon is high-priced. The cost of solar cells formed on polycrystalline silicon is lower than that of the solar cells formed on mono-crystalline silicon and the fabricating processes of the solar cells formed on polycrystalline silicon are easier than that of the solar cells formed on mono-crystalline silicon. However, the polycrystalline silicon solar cell is still difficult to popularize in daily life.
In recent years, organic materials such as polymer utilized to fabricate solar cell are catching academia and industry's attention. Polymer solar cells are fabricated by polymer materials similar with plastic property, and have advantages such as light weight, good flexibility, ruggedness, impact resistance, and low cost. Moreover, polymer solar cells also can be fabricated on a flexible plastic substrate or a thin metal foil substrate, and fabricated by spin-coating or doctor-blading with low cost. In view of these advantages, polymer solar cells are being as noteworthy new generation of solar cells.
Otherwise, the structures of organic polymer solar cells comprise a single-layer structure, a heterojunction structure, and a bulk heterojunction structure which is popular materials in research. The evolution of these structures is for the purpose of obtaining a solar cell device with higher energy conversion power and lowest cost to fabricate. However, promotion of the energy conversion power of single solar cell structure still has restriction. Therefore, a solar cell device which is utilized to stack several solar sub-cells in series/parallel connection is provide for increasing the energy conversion power of a solar cell.
A traditional fabricating method of a solar cell device with stacking several solar sub-cells in series/parallel connection is utilized to stack these solar sub-cells layer by layer. Regarding to FIG. 1, it shows a structure of a solar cell device with stacking several solar sub-cells in series connection. A solar cell device 100 is consisted of a first solar sub-cell 10 and a second solar sub-cell 20. The solar cell device 100 comprises a glass substrate 101 with a transparent conductive oxide layer, and a first solar sub-cell 10 is formed on the glass substrate 101. Then, a silver (Ag) layer 107 is formed on the first solar sub-cell 10, and the silver layer is utilized to provide an electron-hole pair recombination. The second solar sub-cell 20 is further formed on the silver layer 107. The first solar sub-cell 10 and the second solar sub-cell 20 have the same structure, which is consisted of a first heterogeneous material layer 103, 109 and a second heterogeneous material layer 105, 111 respectively, to form a heterogeneous interface. Finally, an exciton barrier layer 113 and a silver electrode 115 are formed on the second solar sub-cell 20.
The traditional fabricating method of the mentioned-above solar cell device 100 is described as below. At first, a glass substrate 101 with a transparent conductive oxide layer is provided. Then, a first heterogeneous material layer 103, a second heterogeneous material layer 105, a silver layer 107, another first heterogeneous 109, another second heterogeneous material layer 111, an exciton barrier layer 113, and silver electrode 115 are formed sequentially on the glass substrate 101. However, this fabricating method of the solar cell device 100 is needed to process in a vacuum environment, and difficult to reduce cost of production.
Furthermore, an organic polymer solar cell can be fabricated by using a simple process to achieve the effect of a large area. However, a multi-layer device fabricated by a solution process will produce solution miscible problem. The solution miscible problem will occur in a coating procedure of a second polymer layer after forming a first polymer layer. The coating procedure of the second polymer layer causes the first polymer layer dissolving such that the interface between of the first polymer layer and the second polymer layer blurred, and the total thickness of the structure also will be less by expectancy, and thereby greatly affecting the quality of the multilayer device.
Moreover, in recent years, the volume of electric device is reduced, and the volume of the accessory battery is also needed to reduce. However, in order to increase the energy conversion power of the mentioned-above solar cell structure formed by stacking in series/parallel connection, the numbers of the stacked solar sub-cells are increased due to the thickness of the solar cell device unable reducing effectively.
Otherwise, the mentioned-above method of stacking several solar sub-cells in series/parallel connection is to stack each solar sub-cell on the substrate sequentially. Therefore, the more solar sub-cells are stacked, the larger thickness of the solar cell device will be produced. Furthermore, the more stacked solar sub-cells also will produce more problems of layer by layer structure, such as the layout of electrodes are also needed to add for electrically connection of each solar sub-cell; or the energy conversion power of the solar cell device doesn't reach the expectancy.
Therefore, there is a need to develop an effective fabricating method of stacking several solar sub-cells in series/parallel connection, and the tandem solar cell device can add its energy conversion power effectively and the quality of the solar cell device can be ensured. Moreover, the fabricating method not only reduces the production cost but also reduces the thickness of the solar cell structure.